The present invention relates to a device for detecting leaks in membranes, etc., for liquid media, whereby the membrane is provided, over at least one partial area of its surface extension, with at least one electrical conductor that produces a change in a measurement signal of the electrical resistance of the conductor when a change occurs on the membrane surface.
Devices of this type are used primarily where liquids are separated from the external environment by membranes, or where membranes are used to conduct liquids. Such applications frequently have very high liquid purity requirements, and the liquid is protected against all possible contamination. This is the case, for example, in the treatment of food, chemicals and other liquids.
A flexible pump membrane that is made of one or more layers of a flexible material is described in European Published Patent Application No. 0 715 690, where one layer is made of a compressed porous polytetrafluoroethylene, in which is embedded an electrically conductive fiber made of an expanded porous polytetrafluoroethylene. The conductive fiber is connected to a monitoring device, and the state of the membrane is monitored by measuring changes in conductivity. However, a membrane of this type, having a fiber embedded in the PTFE layer, is difficult and expensive to manufacture.
It is an object of the present invention to provide a device for detecting leaks in membranes, etc., which is as economical as possible and provides a reliable reading even with very small leaks in the membrane.
According to the general concept of the present invention, therefore, the membrane is provided with a swellable nonwoven that swells when influenced by the liquid through cracks, etc., in the membrane and either joins or separates the electrical conductors provided on the membrane. The conductors are not provided in the membrane itself, but are located on top of the membrane. According to an example embodiment of the membrane, the latter is constructed like a sandwich with at least two layers, and the conductors embedded between two adjacent layers. The conductors may be arranged above one another and separated by an insulator. Depending on whether the swellable nonwoven is to join or separate the conductors, the swellable nonwoven is made of an electrically conductive or nonconductive material.
The swellable nonwoven itself may be inserted as a parallel layer relative to the membrane layers. According to one example embodiment, the membrane is made of an elastomer layer and a PTFE layer, between which the swellable nonwoven and the conductors are embedded, with the swellable nonwoven being adjacent to the PTFE layer.
The foregoing object may be achieved by configuring one conductor as an unbroken surface and the other conductor as a perforated surface. In this case, for example, the membrane layer facing the liquid may be made of PTFE on which a swellable nonwoven is provided. On the swellable nonwoven is placed a first conductor with a perforated surface, followed by an insulating layer with the same perforations. The second conductor with an unbroken surface is provided next, followed by an elastomer layer. The device constructed in this manner is equipped with an electrically conductive swellable nonwoven which swells upon penetration by liquid and enters the perforations in the first conductor and in the insulator until it comes into contact with the second conductor. The two conductive layers of the conductor are joined in this manner, and the corresponding monitoring device displays this state.
According to another example embodiment, the conductors are formed by unbroken surfaces in both layers, with each consecutive surface segment of the conductors contacting each other like bridges so that both conductor layers are joined in an electrically conductive manner. At least in the case of one of the conductors, the spaces between the surface segments are filled with the swellable nonwoven. This swellable nonwoven is made of a nonconductive material. The swellable nonwoven swells as soon as it comes into contact with the liquid and thus separates the two conductor layers, with this state being displayed on the monitoring device.
A device of this type is constructed from a PTFE membrane layer on which is provided a first conductor having surface segments, with swellable nonwoven being inserted between the surface segments, and a second conductor that connects the surface segments like a bridge, after which follows an elastomer membrane layer.
The device according to the present invention is easily manufactured by joining the individual layers, i.e., conductor layers, and gluing or vulcanizing them together. A membrane of this type is also highly resistive as well as being enormously flexible.